Silicon carbide surfaced filaments with titanium carbide coating

ABSTRACT

A composite filament suitable for use as a reinforcement in titanium or nickel matrices comprises a filamentary substrate having a silicon carbide surface layer and a thin, adherent outer layer consisting essentially of titanium carbide.

Galasso et al.

SILICON CARBIDE SURFACED FILAMENTS WITH TITANIUM CARBIDE COATINGInventors: Francis S. Galasso, Manchester;

Bernarr A. Jacob, Torrington, both of Conn.

Appl. No.: 215,593

U.S. C1. 117/69, 117/46 CG, 117/169, 161/172, 161/175 Int. Cl D02g 3/00,D02g 3/02 Field of Search 161/175, 172; 117/46 CB, 117/46 CC, 46 CG, 7]M, 75, 106 C, 128, 69, 169

11 3,811,920 May 21, 1974 [56] References Cited UNITED STATES PATENTS3,306,764 2/1967 Lewis ct a1 117/106 C X 3,366,464 H1968 Guichet ct ul.117/106 C X 3,556,836 1/1971 Basche ct a1 117/106 C X 3,556,837 1/1971Hammond 117/71 M 3,622,369 1 H1971 Basche et a1. 117/46 CG 3,702,26111/1972 Feakes et ul. 117/106 C Primary raminerGe0rge F Lesmes AssistantExaminer-Lorraine T. Kendcll Attorney, Agent, or Firm-John D. Del Ponti5 7 ABSTRACT A composite filament suitable for use as a reinforcement intitanium or nickel matrices comprises a filamentary substrate having asilicon carbide I surface layerand a thin, adherent outer layerconsisting essentially of titanium carbide.

2 Claims, 2 Drawing Figures SILICON CARBIDE SURFACED FILAMENTS WITHTITANIUM CARBIDE COATING BACKGROUND OF THE INVENTION It is known thatsilicon carbide surfaced filaments such as silicon carbide, siliconcarbide coated boron and silicon carbide coated carbon are useful asreinforcing materials in composite structures, particularly siliconcarbide coated boron filaments such as those taught in US. Pat. No.3,622,369, commonly owned by the assignee of the present invention. Inparticular, usefulness of silicon carbide surfaced filaments asreinforcements in the resin matrices and in certain metal matrices suchas aluminum and magnesium is recognized in the industry. While thereactivity of silicon carbide is lower than that of, for example, boron,it has itself been sufficiently high to necessitate the use ofrelatively low temperature or short time at temperature processes duringfabrication of the filament reinforced metal composites in order toprevent fiber degradation. In addition, it limits the choice of metalmatrix material and further, may well define the temperature to whichthe structure is limited in operation.

Accordingly, in power metallurgy or other processes wherein titanium ornickel is hot pressed with silicon carbide surfaced filaments such assilicon carbide coated boron filaments, pressing temperatures have beenheld below about 800C to prevent fiber degradation. While temperaturesbelow 800C can be employed in such a hot pressing technique, theyrequire inordinately high pressures which are not practical for theformation of larger pieces. As a consequence, realization of the fullpotential of silicon carbide surfaced filaments is seen to be dependentupon the development of techniques to enhance fiber matrix compatibilityas hereinbefore discussed.

SUMMARY OF THE INVENTION A The present invention relates to compositefilaments and, more particularly to silicon carbide surfaced filamentssuch as filaments of silicon carbide, silicon carbide coated boron,silicon carbide coated carbon and the like which are provided with athin, adherent coating of titanium carbide.

Titanium carbide has been found to be compatible with silicon carbidesurfaced substrates as well as with such metal matrix materials astitanium and nickel. It has been found that a titanium carbide coatingon a silicon carbide surfaced filament to a thickness of only 0.03 milwill not only impart oxidation resistance to the filament but, inaddition, will provide a diffusion barrier between the silicon carbidesurfaced substrate and such matrix metals as titanium and nickel wherebyfiber degradation is minimized in processes wherein temperatures above800C are employed.

Titanium carbide is advantageous in several respects. Because it mayperform its principal function as surface protection for silicon carbidesurfaced filaments, such as the high modulus, high strength, low densitysilicon carbide coated boron in very thin thicknesses, only a very smallweight penalty is paid as a result of its addition. Furthermore, whilethere is a coefficient of thermal expansion mismatch in the use oftitanium carbide, no problem in this regard has been presented in actualpractice, primarily because of the thin film aspect.

BRIEF DESCRIPTION OF THE DRAWINGS An understanding of the invention willbecome more apparent to those skilled in the art by reference to thefollowing detailed description when viewed in light of the accompanyingdrawings, wherein:

FIG. 1 is a simple sketch, taken in elevation, of apparatus used in theproduction of the titanium carbide coating on the filaments of thepresent invention; and

FIG. 2 is an enlarged cross-sectional view through one of the filamentsof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As seen in FIG. 1, the titaniumcarbide coating is produced on a resistively heated silicon carbidesurface filament 2 which is drawn downwardly through a reactor 4comprising a tubular containment vessel 6, having dual gas inlets 8 and10 at the upper end of the reactor and a single exhaust part 12 at thelower end thereof. Cooling hydrogen is fed to the reactor through inlet8, and inlet 10 is used for the introduction of a reactant gas mixturecomprising methane and titanium chloride (TiCl The containment vesselmay be formed of Pyrex, although a number of other materials includingVycor and quartz will be found satisfactory. The gas inlets 8 and 10 andthe exhaust l2 penetrate and are electrically connected to the metallicend plugs l4and 16 which provide the end closure for the containmentvessel and, also provide convenient means by which power may be suppliedto the wire for resistance heating purposes.

The end plugs are each respectively provided with a well 20 and 22, forcontaining a suitable conductive sealant 24, such as mercury, whichserves the dual purpose of providing a gas seal around the wire where itpenetrates the end plugs, and furtherproviding electrical contactbetween the moving wire and the respective end plugs which are in turnelectrically connected through the tubes 10 and 12 and the leads 26 and28 to a suitable DC power source 30. The upper plug 14 is provided witha peripheral groove 34, which communicates with the mercury well 20through the passageway 36, to provide peripheral sealing around theplug. Sealing between the end plug 16 and the lower end of thecontainment vessel 6 is provided by mercury contained in an annular well38.

The respective plugs are each formed with a centrally oriented orifice40 and 42 which is large enough to accomodate the free passage of thewire 2 therethrough but which, in combination with the wire, is smallenough to retain the mercury, through surface tension forces, in theirrespective wells.

The hydrogen admitted through the inlet 8 enters the reactant chamberimmediately adjacent the wire inlet and is used primarily for coolingpurposes at the end plug 14. As shown in FIG. 2, passage through thereactor results in a composite filament comprising a silicon carbidesurfaced substrate 46 having a thin adherent coating of titanium carbide48. Subsequent to the formation of the titanium carbide layer, thefilaments are consolidated and bonded to the desired matrix material byhot pressing.

Various process techniques and parameters may be utilized in producingfilaments of the present invention, as indicated by the followingexamples.

EXAMPLE I In a reactor of the type illustrated, utilizing an 8 inch longreactor formed from 25 mm Pyrex tubing and a reactant gas mixture ofmethane, hydrogen and titanium chloride, a titanium carbide coating wasproduced on silicon carbide coated boron filaments heated to 1 150C andpassed through the reactor at a rate of 600 ft./hour (reactor dwelltime: 4 seconds). The substrate filaments are commercially availablefrom Hamilton Standard Division of United Aircraft Corporation andcomprised 4 mil boron filaments having a 0.15 mil thick coating ofsilicon carbide and an average UTS of 410,000 psi. The total gas flowthrough the reactor was maintained at 500 cc/min. and the methane wassaturated with TiCl by passing CH through TiCl, in a container andholding the condenser above its container at l8-20C ambient cold watertemperature with the container pressure at l psig. Hydrogen wasintroduced separately into the reactor and the ratio of hydrogen tomethane was maintained at 5 to l.

t The titanium carbide coating was verified by X-ray diffraction andelectrical conductivity measurements showed marked decrease inresistance. The coating was found to be thin (0.03 mils) and adherentwith the.

coated filament exhibiting a UTS of 360,000 psi.

EXAMPLE [I EXAMPLE III The same apparatus and conditions were utilizedas in Example ll except that substrate temperature was l,lOC and thehydrogen/methane 'ratio was to l. Adherent titanium carbide coatingswere approximately 0.02 mils thick, were produced on ten samples and thecomposite coated filament exhibited an average UTS of 372,000 psi.

EXAMPLE IV The same apparatus and conditions were utilized as in ExampleI except that substrate filament speed was 150 ft./hour (reactor dwelltime: 16 seconds), substrate temperature was l,l00C and thehydrogen/methane ratio was 25 to l. The titanium carbide coating was ofsimilar thickness and quality as that produced in Example l andthe'filament had a UTS of 325,000 'psi.

EXAMPLE V Example IV was repeated except that substrate temperature wasl,l50C and the hydrogen/methane ratio was to l. The titanium carbidecoated filament had a UTS of 365,000 psi.

EXAMPLE VI In the reactor apparatus of Example I a thin, adherenttitanium carbide coating is produced on a silicon carbide coated carbonfilament (1 mil circular cross section carbon monofilainent availablefrom Great Lakes Carbon Corporation) heated to l,100C and passed througha reactant gas mixture of methane, hydrogen and titanium chloride in thereactor at a rate of 240 ft./hour (dwell time: 10 seconds). The totalgas flow through the reactor is maintained at 500 cc/min. and thehydrogen/methane ratio is maintained at 5 to l. The methane is saturatedwith TiCl, as in Example I.

EXAMPLE VII Utilizing the apparatus and conditions of Example VI, atitanium carbide coating is produced on a silicon carbide filament p.continuous filament from Dow Corning or General TechnologiesCorporation).

In the course of experimentation, wire temperatures, speeds and gascompositions were varied. It is to be noted that in general, the UTS ofthe filament increases as temperature increases, increases as gas ratioincreases and decreases as dwell time increases. Further, no TiC coatingwas detected by X-ray diffraction when, with a dwell time of 4 seconds,the wire temperature was 1050C and the gas ratio 25 to l or when thewire temperature was ll00C and the ratio 15 to I. Likewise, with thedwell time increased to 10 seconds, no coating could be observed whenthe temperature was maintained at ll50C with a gas ratio of 25 to 1.Finally, with the dwell period at 16 seconds, no coating was observedwhen the temperature was 1050C with a gas ratio of 5 to l.

As indicated in the examples above, the deposition of titanium carbidedoesresult in a small reduction in average strength of the compositefilament. This reduction is relatively slight, however, when the properprocess conditions are observed. The parameters set forth in ExampleIII, for example, show a reduction of only 7 percent (410,000 psi to372,000 psi) in strength. This reduction is not considered significantin view of the fact that the TiC coated filaments allow bonding withtitanium or nickel matrices which normally, at temper atures above 800C,attack and destroy silicon carbide surfaced filaments. In the presentcase, titanium coated filaments were subjected to compatibility testingin matrices of nickel and titanium. Composites were prepared by hotpressing TiC coated silicon carbide surfaced filaments with Ti powder at900C and 5,000 psi for 30 minutes. They were also prepared by hotpressing with Ni powder at 850C and 5,000 psi for 3 minutes. In allcases, the TiC coated filament was not attacked by either the titaniumor the nickel.

While the invention has been described in connection with specificexamples, numerous modifications to the process will be. evident tothose skilled in the art. The examples will, therefore, be understood tobe illustrative only within the true spirit and scope of the inventionas set forth in the appended claims.

What is claimed is:

l. A composite filament for use as a reinforcement in matrices oftitanium and nickel comprising:

a filamentary substrate selected from the group consisting of siliconcarbide, silicon carbide coated boron and silicon carbide coated carbon;and

a thin adherent outer layer which consists essentially of titaniumcarbide.

2. A composite filament according to claim 1 wherein said filamentarysubstrate is a silicon carbide coated boron filament.

l t t t

2. A composite filament according to claim 1 wherein said filamentarysubstrate is a silicon carbide coated boron filament.